The hypothesis of this study is that intravascular ultrasound may provide evaluation of pulmonary vascular changes in pediatric patients with pulmonary hypertension and congenital heart disease presently available only through lung tissue biopsy. The specific aim is that pulmonary vascular changes may be seen by intravascular ultrasound in patients with elevated pulmonary artery pressures whereas, patients w/ normal pulm. artery pressures will not have the degree of proliferative change seen in those pts. with pulmonary hypertension.